1 Lightning is a bright flash of electricity. Lightning is formed by thunderstorms. Not all lightning strikes the ground. Sometimes lightning bolts flash inside a cloud. The negative charges in one part of the cloud reach out to the positive charges in another part of the cloud. This is called an intra-cloud flash. You may have heard the metaphor "a bolt from the blue." It is said about something that came about with no warning. .....For the complete story with questions: click here for printable